The Experts below are selected from a list of 8022 Experts worldwide ranked by ideXlab platform
Luke D. Connell - One of the best experts on this subject based on the ideXlab platform.
-
Evolution of shale apparent permeability under variable boundary conditions
Fuel, 2018Co-Authors: Yan Peng, Zhejun Pan, Jishan Liu, Luke D. ConnellAbstract:Abstract In this study, a general shale apparent permeability model under the influence of gas sorption was derived based on the theory of poroelasticity. Unlike previous models, the impact of gas adsorption-induced Swelling Strain was treated as a local phenomenon. This was achieved through the introduction of an internal Strain. The internal Strain is directionally proportional to the Swelling Strain. The proportional coefficient has a clear physical meaning and is defined as the ratio of the Langmuir Strain constant for shale matrix to the product of the Langmuir Strain constant for shale bulk and the shale porosity. The general permeability model was degenerated into a set of specific shale permeability models under common experimental conditions: (1) constant effective stress; (2) constant pore pressure; and (3) constant confining stress. Nineteen groups of experimental data in the literature were used to verify the validity of those models: three for the boundary condition of constant effective stress; five for the condition of constant pore pressure; and eleven for the boundary condition of constant confining stress. The successful matches of these nineteen groups of experimental data with our model results demonstrate the validity of our general shale permeability. These models can be used to analyze the experimental observations of shale permeability under a spectrum of boundary conditions from constant confining stress to constant pore pressure.
-
Impact of coal matrix Strains on the evolution of permeability
Fuel, 2017Co-Authors: Yan Peng, Zhejun Pan, Luke D. Connell, Jishan Liu, Zhongwei ChenAbstract:The goal of this study is to investigate how coal matrix Strains affect the evolution of coal permeability. In previous studies, this impact was quantified through splitting the matrix Strain into two parts: one contributes to the internal Swelling while the other to the global Strain. It was assumed that the difference between the internal Swelling Strain and the Swelling Strain of matrix determines the evolution of fracture permeability through a constant splitting factor. This assumption means that the impact of internal Swelling Strain is always same during the whole gas injection/production process. This study extends this concept through the introduction of a Strain splitting function that defines the heterogeneous distribution of internal Swelling. The distribution function changes from zero to unity. Zero means that the internal Swelling Strain has no impact on permeability evolution while unity means 100% of the internal Strain contributes to the evolution of coal permeability. Based on this approach, a new permeability model was constructed and a finite element model was built to fully couple the coal deformation and gas transport in coal seam reservoirs. The model was verified against three sets of experimental data under the condition of a constant confining pressure. Model results show that evolution of coal permeability under the condition of a constant confining pressure is primarily controlled by the internal Strain at the early stage, by the global Strain at the later stage, and by the Strain splitting function in-between, and that the impact of the heterogeneous Strain distribution on the internal Swelling Strain vanishes as the Swelling capacity of matrix increases.
-
influence of the effective stress coefficient and sorption induced Strain on the evolution of coal permeability model development and analysis
International Journal of Greenhouse Gas Control, 2012Co-Authors: Luke D. Connell, Zhongwei Chen, Derek ElsworthAbstract:Abstract A series of coal permeability experiments was conducted for coal samples infiltrated both with non-adsorbing and adsorbing gases – all under conditions of constant pressure difference between the confining stress and the pore pressure. The experimental results show that even under controlled stress conditions, coal permeability decreases with respect to pore pressure during the injection of adsorbing gases. This conclusion is apparently not congruent with our conceptual understanding: when coal samples are free to swell/shrink then no effect of Swelling/shrinkage Strain should be apparent on the permeability under controlled stress conditions. In this study, we developed a phenomenological permeability model to explain this enigmatic behavior of coal permeability evolution under the influence of gas sorption by combining the effect of Swelling Strain with that of the mechanical effective stress. For the mechanical effective stress effect, we use the concept of natural Strain to define its impact on the change in fracture aperture; for the Swelling Strain effect, we introduce a partition ratio to define the contribution of Swelling Strain to the fracture aperture reduction. The resulting coal permeability model is defined as a function of both the effective stress and the Swelling Strain. Compared to other commonly used models under specific boundary conditions, such as Palmer–Mansoori (P–M), Shi–Durucan (S–D) and Cui–Bustin (C–B) models, our model results match the experimental measurements quite well. We match the experimental data with the model results for the correct reason, i.e. the model conditions are consistent with the experimental conditions (both are stress-controlled), while other models only match the data for a different reason (the model condition is uniaxial Strain but the experimental condition is stress-controlled). We have also implemented our permeability model into a fully coupled coal deformation and gas transport finite element model to recover the important non-linear responses due to the effective stress effects where mechanical influences are rigorously coupled with the gas transport system.
-
Modeling and Simulation of Moisture Effect on Gas Storage and Transport in Coal Seams
Energy & Fuels, 2012Co-Authors: Dong Chen, Zhejun Pan, Jishan Liu, Luke D. ConnellAbstract:It has been observed in a series of experiments that the presence of moisture in the coal matrix has profound influences on the gas storage and transport in coal seams by reducing the gas adsorption capacity of the coal, decreasing the gas effective diffusivity through the coal matrix, and varying the coal Swelling Strain. A striking piece of evidence of the loss of moisture content in field is the increasing dustiness during the ventilation in coal mining, and this may definitely affect the gas production. However, the combined effect of these processes on coalbed methane production has not been studied in previous works. Therefore, an initial reservoir simulation model has been constructed to investigate the magnitude and interplay of the moisture effect on coalbed methane production. To develop the aforementioned model, approximate relationships have been built to quantify the moisture effect on the gas adsorption capacity, the gas effective diffusivity and the coal Swelling Strain. These relationships...
-
Coal Swelling Strain and permeability change with injecting liquid/supercritical CO2 and N2 at stress-conStrained conditions
International Journal of Coal Geology, 2011Co-Authors: Tamotsu Kiyama, Soshi Nishimoto, Masaji Fujioka, Ziqiu Xue, Yoji Ishijima, Zhejun Pan, Luke D. ConnellAbstract:Abstract CO 2 sequestration in deep unmineable coalbeds is regarded as a viable option for carbon storage. On the other hand, many uncertainties still remain due to the fact that coal interacts with CO 2 in a variety of ways. In Japan, the first CO 2 Enhanced Coalbed Methane Recovery field trials at Yubari were carried out. CO 2 was injected from an injection well into a coalbed at a depth of 900 m, and coalbed methane was collected from an observation well. Since the CO 2 injection rate was an order of magnitude lower than that estimated by preliminary analyses, N 2 was injected in an attempt to improve it. However, this caused only a temporary increase in the CO 2 injection rate. To better understand the phenomena observed in the Yubari field tests, two laboratory experiments were conducted under stress-conStrained conditions. In Test I, liquid CO 2 was injected into a water-saturated coal specimen and then heated and injected as supercritical CO 2 . This was to simulate the initial stage of CO 2 injection at Yubari when the coal seam was saturated with water. In Test II, supercritical CO 2 was injected into a coal specimen saturated with N 2 , and then N 2 and CO 2 were repeatedly injected. This test was to simulate the case of N 2 injection and CO 2 re-injection at Yubari. In Test I, a volumetric Swelling Strain of 0.25 to 0.5% was observed after injecting liquid CO 2 . However, in Test II, the Swelling Strain was about 0.5 to 0.8% after injecting supercritical CO 2 . Following further injection of N 2 in Test II, slow Strain recovery was observed in the coal. At an effective stress of 2 MPa, the permeability of the water-saturated coal specimen was 2 × 10 − 6 darcy. In contrast, the permeability of the N 2 -saturated coal specimen was originally 5 × 10 − 4 to 9 × 10 − 4 darcy, and after injection of supercritical CO 2 it decreased to 2 × 10 − 4 darcy. Further injections of N 2 and supercritical CO 2 caused little subsequent change in permeability. These results suggest that when liquid CO 2 was injected into the water-saturated coal specimen, it did not completely displace the water in the coal matrix. To further investigate the coal Swelling and permeability behavior during gas injection, elastic wave velocity measurements were carried out and the results were found to validate those obtained using Strain gauges. The results indicate that coal Swelling is likely to be the main cause for the permeability change in the Yubari field tests and thus provide useful information for modeling the field trial.
Bao Chen - One of the best experts on this subject based on the ideXlab platform.
-
influence of pore fluid concentration on water retention properties of compacted gmz01 bentonite
Applied Clay Science, 2016Co-Authors: Yong He, Yonggui Chen, Weimin Ye, Bao Chen, B. YeAbstract:Abstract Due to its low hydraulic conductivity, high Swelling capacity and good adsorption properties, the Gaomiaozi (GMZ) bentonite has been proposed as a suitable buffer/backfill material for the construction of artificial barriers in a deep geological repository for the disposal of high-level nuclear waste (HLW) in China. Compacted GMZ01 bentonite with an initial dry density of 1.70 g/cm 3 was hydrated with distilled water and NaCl solutions. The Swelling Strain was recorded. After being saturated, suction-controlled drying tests were conducted and corresponding soil water retention curves were obtained. MIP investigations were conducted on the void ratio variation of a specimen before and after experiencing wetting and drying processes. Results show that the Swelling Strain of compacted GMZ01 bentonite decreases as the concentration of infiltration solution increases. The shrinkage curve of saturated compacted GMZ01 bentonite specimens evolves with controlling suctions and could be divided into three stages including a normal shrinkage stage, a residual shrinkage stage and a zero shrinkage stage. For a given suction, the measured void ratio of a specimen saturated with distilled water is slightly larger than those of specimens saturated with salt solutions after the drying equilibrium is reached. For a given suction, the degree of saturation of a compacted GMZ01 bentonite specimen increases as the salt concentration increases. According to the test results, a modified SWRC equation was proposed to account for the effect of void ratio and salt solutions on drying behaviour. The verified results revealed that the proposed equation can satisfactorily describe the SWRCs of compacted GMZ01 bentonite saturated with different solutions.
-
Effects of solution concentration and vertical stress on the Swelling behavior of compacted GMZ01 bentonite
Applied Clay Science, 2016Co-Authors: Yonggui Chen, Yu-jun Cui, Chun-min Zhu, Bao ChenAbstract:Abstract Compacted bentonite has been considered as buffer/backfill material in radioactive waste disposal. This study deals with the effects of the concentration of infiltration saturation and vertical stress on the Swelling behavior of compacted GMZ bentonite. One-dimensional Swelling tests were performed on specimens at an initial dry density of 1.7 Mg/m 3 . NaCl solutions with concentrations of 0 (de-ionized water), 0.1, 0.5 and 1.0 mol/L were used to saturate the specimens while three vertical stresses of 0.06, 0.062 and 1.85 MPa were applied. Results show that, for all the infiltration solutions, the Swelling Strain decreases with increasing vertical stress; the impact of the vertical stress is more significant for low vertical loads while it is less patent when the high salinity solution is infiltrated. For all the vertical stresses applied, the Swelling Strain decreases with the increase in concentration of the infiltration solution; the impact of the concentration of infiltration solution is not only related to the vertical stress, but also to the soil permeability. Furthermore, the coefficient of primary Swelling decreases with the increase in concentration and vertical stress. The concentration of infiltration solution has significant restricting effect on the secondary Swelling deformation in case of low vertical stress, while it has no or few effects on the secondary Swelling deformation in case of higher vertical stress.
-
Influences of salt solution concentration and vertical stress during saturation on the volume change behavior of compacted GMZ01 bentonite
Engineering Geology, 2016Co-Authors: Feng Zhang, Yonggui Chen, Bao Chen, Yu-jun CuiAbstract:Abstract Investigation of the effects of salt solution concentration and vertical stress during saturation on the volume change behavior of compacted bentonite is of great importance for the assessment of the behavior of engineering barrier in deep geological repository for disposal of high-level radioactive waste. In this study, oedometer tests were conducted on densely compacted GMZ01 bentonite specimens with an initial dry density of 1.70 Mg/m 3 , which experienced Swelling under different vertical stresses with infiltration of de-ionized water or NaCl solutions at different concentrations. The effects of salt solution concentration and vertical stress during saturation on the volume change of GMZ01 bentonite specimens were investigated in terms of Swelling Strain, elastic compressibility parameter, plastic compressibility parameter and yield stress. Results show that as the concentrations of salt solutions increase, the Swelling Strain, the elastic compressibility parameter and the plastic compressibility parameter decrease, while the yield stress increases. However, the vertical stress during saturation can only affect the Swelling Strain and the yield stress. Based on the test results, empirical equations with consideration of salt solution concentration and vertical stress during saturation effects were proposed allowing the prediction of Swelling Strain, plastic compressibility parameter and yield stress. The calculated results are in good agreement with the experimental ones.
-
Influences of salt solution concentration vertical stress during saturation on the volume change behavior of compacted GMZ01 bentonite
Engineering Geology, 2016Co-Authors: Feng Zhang, Yonggui Chen, Bao Chen, Yu-jun CuiAbstract:Investigation of the effects of salt solution concentration vertical stress during saturation on the volume change behavior of compacted bentonite is of great importance for the assessment of the behavior of engineering barrier in deep geological repository for disposal of high-level radioactive waste. In this study, oedometer tests were conducted on densely compacted GMZ01 bentonite specimens with an initial dry density of 1.70 Mg/m(3), which experienced Swelling under different vertical stresses with infiltration of de-ionized water or NaCl solutions at different concentrations. The effects of salt solution concentration vertical stress during saturation on the volume change of GMZ01 bentonite specimens were investigated in terms of Swelling Strain, elastic compressibility parameter, plastic compressibility parameter yield stress. Results show that as the concentrations of salt solutions increase, the Swelling Strain, the elastic compressibility parameter the plastic compressibility parameter decrease, while the yield stress increases. However, the vertical stress during saturation can only affect the Swelling Strain the yield stress. Based on the test results, empirical equations with consideration of salt solution concentration vertical stress during saturation effects were proposed allowing the prediction of Swelling Strain, plastic compressibility parameter yield stress. The calculated results are in good agreement with the experimental ones. (C) 2016 Elsevier B.V. All rights reserved.
-
Effects of solution concentration vertical stress on the Swelling behavior of compacted GMZ01 bentonite
Applied Clay Science, 2016Co-Authors: Yonggui Chen, Yu-jun Cui, Chun-min Zhu, Bao ChenAbstract:Compacted bentonite has been considered as buffer/backfill material in radioactive waste disposal. This study deals with the effects of the concentration of infiltration saturation vertical stress on the Swelling behavior of compacted GMZ bentonite. One-dimensional Swelling tests were performed on specimens at an initial dry density of 1.7 Mg/m(3). NaCl solutions with concentrations of 0 (de-ionized water), 0.1, 0.5 1.0 mol/L were used to saturate the specimens while three vertical stresses of 0.06, 0.062 1.85 MPa were applied. Results show that, for all the infiltration solutions, the Swelling Strain decreases with increasing vertical stress; the impact of the vertical stress is more significant for low vertical loads while it is less patent when the high salinity solution is infiltrated. For all the vertical stresses applied, the Swelling Strain decreases with the increase in concentration of the infiltration solution; the impact of the concentration of infiltration solution is not only related to the vertical stress, but also to the soil permeability. Furthermore, the coefficient of primary Swelling decreases with the increase in concentration vertical stress. The concentration of infiltration solution has significant restricting effect on the secondary Swelling deformation in case of low vertical stress, while it has no or few effects on the secondary Swelling deformation in case of higher vertical stress. (C) 2016 Elsevier B.V. All rights reserved.
Yu-jun Cui - One of the best experts on this subject based on the ideXlab platform.
-
Swelling deformation of Gaomiaozi bentonite under alkaline chemical conditions in a repository
Engineering Geology, 2020Co-Authors: Zhao Sun, Yonggui Chen, Yu-jun Cui, Qiong WangAbstract:Abstract The safety assessment for the long-term operation of a deep repository is an essential work for the engineering of geological disposal for high-level radioactive waste (HLW). Bentonite selected as a barrier/backfill material in repositories, can be exposed to the chemical effects of alkaline site water owing to cement degradation, which poses a great threat to the long-term safety of the repository. This work is focusing on the Swelling property of bentonite with alkaline pore water in order to investigate the evolution of vertical Strain of compacted Gaomiaozi bentonite under the simulated long-term environments of Chinese HLW repository. Fourier transform infrared spectroscopy, X-ray powder diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy tests were utilized to analyze the bentonite after it reacted with the pore water solutions. Results reveal that the Swelling Strain is significantly influenced by the composition and concentration of the solutions, and that Swelling time decreases as temperature increases. In the secondary Swelling stage of the bentonite hydrated by solutions containing K+, the Swelling Strain decays because K ions enter the montmorillonite crystal layer and generate low-Swelling or non-Swelling minerals. The solutions (particularly high alkaline solutions) containing K ions strongly decrease the Swelling performance of bentonite, suggesting that alkaline cement water can degrade the Swelling property of the buffer material in a high-level radioactive waste (HLW) disposal system.
-
Mechanical behavior of GMZ bentonite pellet mixtures over a wide suction range
Engineering Geology, 2020Co-Authors: Zhao Zhang, Qiong Wang, Zhang-rong Liu, Yu-jun CuiAbstract:High-density bentonite pellet mixtures have been proposed as candidate materials for filling technological voids in the deep geological disposal repository of high-level radioactive waste (HLW). Water vapour transfer plays a major role in the function formation of the unsaturated engineering barrier system, due to the existing high thermal gradients generated by the decay heat released from the canister. In this work, series of suction controlled Swelling pressure tests, Swelling deformation tests and compression tests were conducted on GMZ bentonite pellet mixtures. Results show that, for the specimen hydrated by the vapour equilibrium technique, no collapse was observed on the evolution curve of Swelling pressure. However, for that wetted by the osmotic technique, a collapse of Swelling pressure was observed after the first peak value. For specimens hydrated with suction-control, a collapse on the evolution curve of Swelling Strain was only observed under high vertical stresses. In addition, the unloading curves of specimens exhibited a linearity at the high suction stage and a bi-linearity at the low suction stage. The Swelling pressure determined by the swell-consolidation method was higher than that determined by the constant-volume method.
-
Effects of K+ solutions on Swelling behavior of compacted GMZ bentonite
Engineering Geology, 2019Co-Authors: Yonggui Chen, Yu-jun CuiAbstract:During the long-term operation of a deep geological repository, the buffer/backfill properties of compacted bentonite could be affected by the chemistry of the infiltrated porewater. In this study, Swelling tests and microstructural analyses were conducted on the compacted GMZ bentonite specimens with an initial dry density of 1.5 or 1.7 Mg/m3 with infiltration of distilled water, as well as, KCl and KOH solutions (0.1 and 1.0 M). Influences of K+ solutions on the Swelling behavior of compacted GMZ bentonite were investigated. Results show that Swelling properties of compacted GMZ bentonite specimens could be significantly influenced by concentration of K+ solutions and dry density of specimens. Swelling pressure of compacted GMZ bentonite specimens was significantly attenuated by infiltration of K+ salt/alkaline solutions. For Swelling Strain tests with infiltration of KCl or KOH solutions, instead of a secondary Swelling stage, a volumetric collapse stage was observed. Micro-structural test results demonstrate that the attenuation of Swelling behavior could be attributed to the K+ exchange or silica dissolution.
-
Effects of solution concentration and vertical stress on the Swelling behavior of compacted GMZ01 bentonite
Applied Clay Science, 2016Co-Authors: Yonggui Chen, Yu-jun Cui, Chun-min Zhu, Bao ChenAbstract:Abstract Compacted bentonite has been considered as buffer/backfill material in radioactive waste disposal. This study deals with the effects of the concentration of infiltration saturation and vertical stress on the Swelling behavior of compacted GMZ bentonite. One-dimensional Swelling tests were performed on specimens at an initial dry density of 1.7 Mg/m 3 . NaCl solutions with concentrations of 0 (de-ionized water), 0.1, 0.5 and 1.0 mol/L were used to saturate the specimens while three vertical stresses of 0.06, 0.062 and 1.85 MPa were applied. Results show that, for all the infiltration solutions, the Swelling Strain decreases with increasing vertical stress; the impact of the vertical stress is more significant for low vertical loads while it is less patent when the high salinity solution is infiltrated. For all the vertical stresses applied, the Swelling Strain decreases with the increase in concentration of the infiltration solution; the impact of the concentration of infiltration solution is not only related to the vertical stress, but also to the soil permeability. Furthermore, the coefficient of primary Swelling decreases with the increase in concentration and vertical stress. The concentration of infiltration solution has significant restricting effect on the secondary Swelling deformation in case of low vertical stress, while it has no or few effects on the secondary Swelling deformation in case of higher vertical stress.
-
Influences of salt solution concentration and vertical stress during saturation on the volume change behavior of compacted GMZ01 bentonite
Engineering Geology, 2016Co-Authors: Feng Zhang, Yonggui Chen, Bao Chen, Yu-jun CuiAbstract:Abstract Investigation of the effects of salt solution concentration and vertical stress during saturation on the volume change behavior of compacted bentonite is of great importance for the assessment of the behavior of engineering barrier in deep geological repository for disposal of high-level radioactive waste. In this study, oedometer tests were conducted on densely compacted GMZ01 bentonite specimens with an initial dry density of 1.70 Mg/m 3 , which experienced Swelling under different vertical stresses with infiltration of de-ionized water or NaCl solutions at different concentrations. The effects of salt solution concentration and vertical stress during saturation on the volume change of GMZ01 bentonite specimens were investigated in terms of Swelling Strain, elastic compressibility parameter, plastic compressibility parameter and yield stress. Results show that as the concentrations of salt solutions increase, the Swelling Strain, the elastic compressibility parameter and the plastic compressibility parameter decrease, while the yield stress increases. However, the vertical stress during saturation can only affect the Swelling Strain and the yield stress. Based on the test results, empirical equations with consideration of salt solution concentration and vertical stress during saturation effects were proposed allowing the prediction of Swelling Strain, plastic compressibility parameter and yield stress. The calculated results are in good agreement with the experimental ones.
Yonggui Chen - One of the best experts on this subject based on the ideXlab platform.
-
Swelling deformation of Gaomiaozi bentonite under alkaline chemical conditions in a repository
Engineering Geology, 2020Co-Authors: Zhao Sun, Yonggui Chen, Yu-jun Cui, Qiong WangAbstract:Abstract The safety assessment for the long-term operation of a deep repository is an essential work for the engineering of geological disposal for high-level radioactive waste (HLW). Bentonite selected as a barrier/backfill material in repositories, can be exposed to the chemical effects of alkaline site water owing to cement degradation, which poses a great threat to the long-term safety of the repository. This work is focusing on the Swelling property of bentonite with alkaline pore water in order to investigate the evolution of vertical Strain of compacted Gaomiaozi bentonite under the simulated long-term environments of Chinese HLW repository. Fourier transform infrared spectroscopy, X-ray powder diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy tests were utilized to analyze the bentonite after it reacted with the pore water solutions. Results reveal that the Swelling Strain is significantly influenced by the composition and concentration of the solutions, and that Swelling time decreases as temperature increases. In the secondary Swelling stage of the bentonite hydrated by solutions containing K+, the Swelling Strain decays because K ions enter the montmorillonite crystal layer and generate low-Swelling or non-Swelling minerals. The solutions (particularly high alkaline solutions) containing K ions strongly decrease the Swelling performance of bentonite, suggesting that alkaline cement water can degrade the Swelling property of the buffer material in a high-level radioactive waste (HLW) disposal system.
-
Effects of K+ solutions on Swelling behavior of compacted GMZ bentonite
Engineering Geology, 2019Co-Authors: Yonggui Chen, Yu-jun CuiAbstract:During the long-term operation of a deep geological repository, the buffer/backfill properties of compacted bentonite could be affected by the chemistry of the infiltrated porewater. In this study, Swelling tests and microstructural analyses were conducted on the compacted GMZ bentonite specimens with an initial dry density of 1.5 or 1.7 Mg/m3 with infiltration of distilled water, as well as, KCl and KOH solutions (0.1 and 1.0 M). Influences of K+ solutions on the Swelling behavior of compacted GMZ bentonite were investigated. Results show that Swelling properties of compacted GMZ bentonite specimens could be significantly influenced by concentration of K+ solutions and dry density of specimens. Swelling pressure of compacted GMZ bentonite specimens was significantly attenuated by infiltration of K+ salt/alkaline solutions. For Swelling Strain tests with infiltration of KCl or KOH solutions, instead of a secondary Swelling stage, a volumetric collapse stage was observed. Micro-structural test results demonstrate that the attenuation of Swelling behavior could be attributed to the K+ exchange or silica dissolution.
-
Thermodynamic Response of Crystalline Swelling and Double-Layer Swelling of Compacted Bentonite
Proceedings of GeoShanghai 2018 International Conference: Multi-physics Processes in Soil Mechanics and Advances in Geotechnical Testing, 2018Co-Authors: Yonggui ChenAbstract:Strong thermodynamic disequilibrium existed in HLW repository site often deteriorates the hydration Swelling capacity of compacted bentonite, including the crystalline Swelling and the double-layer Swelling. In order to investigate the temperature effect on the crystalline Swelling capacity and the double-layer Swelling capacity, four Swelling pressure tests and four Swelling Strain tests were conducted on compacted Gaomiaozi (GMZ) bentonite specimens saturated with de-ionized water under the temperature of 20 °C to 80 °C. Main observations show that the crystalline Swelling capacity and the double-layer Swelling capacity generally decrease with the temperature increases; whereas the crystalline Swelling pressure and the double-layer Swelling Strain present a slight increase tendency under higher temperatures, especially the temperature 60 °C and 80 °C.
-
influence of pore fluid concentration on water retention properties of compacted gmz01 bentonite
Applied Clay Science, 2016Co-Authors: Yong He, Yonggui Chen, Weimin Ye, Bao Chen, B. YeAbstract:Abstract Due to its low hydraulic conductivity, high Swelling capacity and good adsorption properties, the Gaomiaozi (GMZ) bentonite has been proposed as a suitable buffer/backfill material for the construction of artificial barriers in a deep geological repository for the disposal of high-level nuclear waste (HLW) in China. Compacted GMZ01 bentonite with an initial dry density of 1.70 g/cm 3 was hydrated with distilled water and NaCl solutions. The Swelling Strain was recorded. After being saturated, suction-controlled drying tests were conducted and corresponding soil water retention curves were obtained. MIP investigations were conducted on the void ratio variation of a specimen before and after experiencing wetting and drying processes. Results show that the Swelling Strain of compacted GMZ01 bentonite decreases as the concentration of infiltration solution increases. The shrinkage curve of saturated compacted GMZ01 bentonite specimens evolves with controlling suctions and could be divided into three stages including a normal shrinkage stage, a residual shrinkage stage and a zero shrinkage stage. For a given suction, the measured void ratio of a specimen saturated with distilled water is slightly larger than those of specimens saturated with salt solutions after the drying equilibrium is reached. For a given suction, the degree of saturation of a compacted GMZ01 bentonite specimen increases as the salt concentration increases. According to the test results, a modified SWRC equation was proposed to account for the effect of void ratio and salt solutions on drying behaviour. The verified results revealed that the proposed equation can satisfactorily describe the SWRCs of compacted GMZ01 bentonite saturated with different solutions.
-
Effects of solution concentration and vertical stress on the Swelling behavior of compacted GMZ01 bentonite
Applied Clay Science, 2016Co-Authors: Yonggui Chen, Yu-jun Cui, Chun-min Zhu, Bao ChenAbstract:Abstract Compacted bentonite has been considered as buffer/backfill material in radioactive waste disposal. This study deals with the effects of the concentration of infiltration saturation and vertical stress on the Swelling behavior of compacted GMZ bentonite. One-dimensional Swelling tests were performed on specimens at an initial dry density of 1.7 Mg/m 3 . NaCl solutions with concentrations of 0 (de-ionized water), 0.1, 0.5 and 1.0 mol/L were used to saturate the specimens while three vertical stresses of 0.06, 0.062 and 1.85 MPa were applied. Results show that, for all the infiltration solutions, the Swelling Strain decreases with increasing vertical stress; the impact of the vertical stress is more significant for low vertical loads while it is less patent when the high salinity solution is infiltrated. For all the vertical stresses applied, the Swelling Strain decreases with the increase in concentration of the infiltration solution; the impact of the concentration of infiltration solution is not only related to the vertical stress, but also to the soil permeability. Furthermore, the coefficient of primary Swelling decreases with the increase in concentration and vertical stress. The concentration of infiltration solution has significant restricting effect on the secondary Swelling deformation in case of low vertical stress, while it has no or few effects on the secondary Swelling deformation in case of higher vertical stress.
Zhejun Pan - One of the best experts on this subject based on the ideXlab platform.
-
Evolution of shale apparent permeability under variable boundary conditions
Fuel, 2018Co-Authors: Yan Peng, Zhejun Pan, Jishan Liu, Luke D. ConnellAbstract:Abstract In this study, a general shale apparent permeability model under the influence of gas sorption was derived based on the theory of poroelasticity. Unlike previous models, the impact of gas adsorption-induced Swelling Strain was treated as a local phenomenon. This was achieved through the introduction of an internal Strain. The internal Strain is directionally proportional to the Swelling Strain. The proportional coefficient has a clear physical meaning and is defined as the ratio of the Langmuir Strain constant for shale matrix to the product of the Langmuir Strain constant for shale bulk and the shale porosity. The general permeability model was degenerated into a set of specific shale permeability models under common experimental conditions: (1) constant effective stress; (2) constant pore pressure; and (3) constant confining stress. Nineteen groups of experimental data in the literature were used to verify the validity of those models: three for the boundary condition of constant effective stress; five for the condition of constant pore pressure; and eleven for the boundary condition of constant confining stress. The successful matches of these nineteen groups of experimental data with our model results demonstrate the validity of our general shale permeability. These models can be used to analyze the experimental observations of shale permeability under a spectrum of boundary conditions from constant confining stress to constant pore pressure.
-
Impact of coal matrix Strains on the evolution of permeability
Fuel, 2017Co-Authors: Yan Peng, Zhejun Pan, Luke D. Connell, Jishan Liu, Zhongwei ChenAbstract:The goal of this study is to investigate how coal matrix Strains affect the evolution of coal permeability. In previous studies, this impact was quantified through splitting the matrix Strain into two parts: one contributes to the internal Swelling while the other to the global Strain. It was assumed that the difference between the internal Swelling Strain and the Swelling Strain of matrix determines the evolution of fracture permeability through a constant splitting factor. This assumption means that the impact of internal Swelling Strain is always same during the whole gas injection/production process. This study extends this concept through the introduction of a Strain splitting function that defines the heterogeneous distribution of internal Swelling. The distribution function changes from zero to unity. Zero means that the internal Swelling Strain has no impact on permeability evolution while unity means 100% of the internal Strain contributes to the evolution of coal permeability. Based on this approach, a new permeability model was constructed and a finite element model was built to fully couple the coal deformation and gas transport in coal seam reservoirs. The model was verified against three sets of experimental data under the condition of a constant confining pressure. Model results show that evolution of coal permeability under the condition of a constant confining pressure is primarily controlled by the internal Strain at the early stage, by the global Strain at the later stage, and by the Strain splitting function in-between, and that the impact of the heterogeneous Strain distribution on the internal Swelling Strain vanishes as the Swelling capacity of matrix increases.
-
Experimental study of Swelling of organic rich shale in methane
International Journal of Coal Geology, 2015Co-Authors: Tianyu Chen, Xia-ting Feng, Zhejun PanAbstract:Abstract Gas is stored in shale mainly in free and adsorbed phases. Since a significant amount of gas in the shale is adsorbed to the organic matter and/or clay minerals, it is possible that gas adsorption will induce shale Swelling, which may then has an impact on the gas flow behavior in the shale thus its gas production. In this work, Strain behavior was studied in two gases, helium and methane, at different pore pressures under constant hydrostatic pressure at 20 MPa on two shale samples. The results show that porosity and volumetric Strain are functions of gas pressure and the Strain is larger in methane than helium demonstrating gas adsorption induced Swelling for the shale samples. The calculated methane adsorption induced Swelling Strain is at a magnitude of 0.1% volumetrically with pressure at 10 MPa for the shale samples studied. The adsorption induced shale Swelling Strain shows a Langmuir-like relationship with pressure and is proportional to the amount of methane adsorbed. The results also show slight anisotropic Strain behavior between the two directions of parallel and perpendicular to the bedding and Strain hysteresis with methane in and out of the shale. The gas adsorption induced Swelling may influence gas flow in gas shale, thus more research in this topic is warranted.
-
Modeling and Simulation of Moisture Effect on Gas Storage and Transport in Coal Seams
Energy & Fuels, 2012Co-Authors: Dong Chen, Zhejun Pan, Jishan Liu, Luke D. ConnellAbstract:It has been observed in a series of experiments that the presence of moisture in the coal matrix has profound influences on the gas storage and transport in coal seams by reducing the gas adsorption capacity of the coal, decreasing the gas effective diffusivity through the coal matrix, and varying the coal Swelling Strain. A striking piece of evidence of the loss of moisture content in field is the increasing dustiness during the ventilation in coal mining, and this may definitely affect the gas production. However, the combined effect of these processes on coalbed methane production has not been studied in previous works. Therefore, an initial reservoir simulation model has been constructed to investigate the magnitude and interplay of the moisture effect on coalbed methane production. To develop the aforementioned model, approximate relationships have been built to quantify the moisture effect on the gas adsorption capacity, the gas effective diffusivity and the coal Swelling Strain. These relationships...
-
Modeling of coal Swelling induced by water vapor adsorption
Frontiers of Chemical Science and Engineering, 2012Co-Authors: Zhejun PanAbstract:Gas adsorption-induced coal Swelling is a well-know phenomenon. Coal Swelling or shrinkage by adsorption or desorption of water vapor has not been well understood but has significant implications on gas drainage process for underground coal mining and for primary and enhanced coalbed methane production. Decreased matrix moisture content leads to coal shrinkage and thus the change of cleat porosity and permeability under reservoir conditions. Unlike gas adsorption in coal which usually forms a single layer of adsorbed molecules, water vapor adsorption in the coal micropores forms multilayer of adsorbed molecules. In this work, a model has been developed to describe the coal Swelling Strain with respect to the amount of moisture intake by the coal matrix. The model extended an energy balance approach for gas adsorption-induced coal Swelling to water vapor adsorption-induced coal Swelling, assuming that only the first layer of adsorbed molecules of the multilayer adsorption changes the surface energy, which thus causes coal to swell. The model is applied to describe the experimental Swelling Strain data measured on an Australian coal. The results show good agreement between the model and the experimental data.
